In this project we will study the intracellular synthesis of murine mammary tumor virus (MuMTV) proteins including reverse transcriptase in a virus-producing mouse mammary tumor cell line and a feline kidney cell line infected with MuMTV. With the help of monospecific sera to MuMTV proteins, we intend to isolate and identify virus-specific precursor proteins from these cells by radioimmunoprecipitation followed by gel electrophoresis. These studies will also reveal a possible role for the host cell in the processing of MuMTV precursor proteins will be investigated by treating MuMTV infected cells with amino acid analogs and protease inhibitors. The effects of glucocorticoid hormones on the synthesis and processing of the viral precursor proteins will also be studied. Tissue culture grown MuMTV and MuMTV derived from milk, which exhibit striking differences in their surface morphology, will be examined to see if they also have biochemical and/or biological differences. We will identify those MuMTV proteins which are present on the surface of intact virus and viral core using immunoelectron microscopic techniques. Using radioimmunocompetition assays, we will attempt to identify the type and group specific antigens shared by MuMTV derived from different strains of mice. Virus and virus producing cells will studied by immunoelectron microscopy in order to determine which of the MuMTV specific antigens are present on the viral and cell surface. We will also determine whether or not mice can be protected from the development of naturally occurring mammary tumors by immunization with the major envelope glycoprotein of MuMTV. The structural analysis of MuMTV and elucidation of the mechanisms involved in the processing of the viral proteins will provide valuable information about the interaction between the murine mammary tumor virus and the cells it infects.